Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $65.49   11.507%   $73.0259   $73.03   $73.05   $73.00  
  Purchase #2 $59.83   6.308%   $63.6041   $63.60   $63.60   $63.60  
  Purchase #3 $149.77   3.470%   $154.967   $154.97   $154.95   $155.00  
  Purchase #4 $148.46   4.855%   $155.6677   $155.67   $155.65   $155.70  
  Purchase #5 $74.40   7.452%   $79.9443   $79.94   $79.95   $79.90  
  Purchase #6 $233.31   12.476%   $262.4178   $262.42   $262.40   $262.40  
  Purchase #7 $154.83   8.781%   $168.4256   $168.43   $168.45   $168.40  
  7 purchase totals = $886.09       $958.0524   $958.06   $958.05   $958.00